18.1 Conditional Commands

Texinfo has an @ifformat environment for each output
format, to allow conditional inclusion of text for a particular output
format.

@ifinfo begins segments of text that should be ignored by
TeX when it typesets the printed manual, and by makeinfo
when not producing Info output. The segment of text appears only in
the Info file and, for historical compatibility, the plain text
output.

The environments for the other formats are analogous, but without the
special historical case:

@ifdocbook … @end ifdocbook

Text to appear only in the Docbook output.

@ifhtml … @end ifhtml

Text to appear only in the HTML output.

@ifplaintext … @end ifplaintext

Text to appear only in the plain text output.

@iftex … @end iftex

Text to appear only in the printed manual.

@ifxml … @end ifxml

Text to appear only in the XML output.

The @if… and @end if… commands must appear
on lines by themselves in your source file. The newlines following
the commands are (more or less) treated as whitespace, so that the
conditional text is flowed normally into a surrounding paragraph.

The @if… constructs are intended to conditionalize
normal Texinfo source; see Raw Formatter Commands, for using
underlying format commands directly.

Here is an example showing all these conditionals:

@iftex
This text will appear only in the printed manual.
@end iftex
@ifinfo
However, this text will appear only in Info and plain text.
@end ifinfo
@ifhtml
And this text will only appear in HTML.
@end ifhtml
@ifplaintext
Whereas this text will only appear in plain text.
@end ifplaintext
@ifxml
Notwithstanding that this will only appear in XML.
@end ifxml
@ifdocbook
Nevertheless, this will only appear in Docbook.
@end ifdocbook

The preceding example produces the following line:

And this text will only appear in HTML.

Notice that you only see one of the input lines, depending on which
version of the manual you are reading.

In complex documents, you may want Texinfo to issue an error message
in some conditionals that should not ever be processed. The
@errormsg{text} command will do this; it takes one
argument, the text of the error message, which is expanded more or
less as if it were Info text.

We mention @errormsg{} here even though it is not strictly
related to conditionals, since in practice it is most likely to be
useful in that context. Technically, it can be used anywhere.
See External Macro Processors, for a caveat regarding the line
numbers which @errormsg emits in TeX.